American-style Transformer Substation Load Switch

In American-style prefabricated substations, the load switch is placed inside the transformer tank. Oil-immersed three-phase interlocking switches are available in two-position (terminal type) and four-position (ring network type) configurations. Because this load switch is located inside the transformer tank, its open/closed position can only be determined by the indication on the external control panel, and its operation requires a dedicated insulated operating rod, making it relatively complex. From this perspective, its operation is quite inconvenient. Furthermore, since the opening contacts (i.e., the obvious disconnection point) of the load switch are not visible, it creates a sense of unease after disconnection. Moreover, if the load switch malfunctions, replacement and repair will be extremely difficult. Load switches generally use vacuum circuit breakers.

American-style prefabricated substations lack oil temperature protection; they only have a thermometer to display the oil temperature. When the oil temperature is too high, protection is provided by a plug-in fuse, and a pressure relief valve is used to release excessive pressure within the tank. Therefore, it is essential to regularly check whether the fuse is operating normally under these two conditions and whether there is any oil leakage from the casing.